Hundreds of supermarkets across France have been hit by a cyberattack that caused refrigeration units to overheat, resulting in the spoilage of fresh and frozen food estimated to be worth millions of euros.

The hackers reportedly gained control of the software regulating the temperatures of refrigeration units, causing some to reach 50C (120F) overnight.

The chief executive of Coopérative U described the incident as an “extremely serious and unprecedented” attack, saying several of the chain’s supermarkets had been affected.

According to AFP, more than 100 Coopérative U supermarkets were targeted, while at least 300 stores operated by Intermarché and its Netto discount brand were also affected.

Reuters reported that Intermarché’s refrigerators reached temperatures of 50C for six hours overnight into Monday. The retailer said it had discarded all affected food to prevent potential health risks.

Some supermarket workers reportedly encountered waves of hot air when they opened freezer units on Monday morning.

French broadcaster BFMTV published an image showing a freezer in an ice cream aisle displaying a temperature of 26.5C.

The broadcaster also reported that two supermarkets in the Alsace region suffered combined losses of €270,000 (£228,000), raising concerns that the total financial damage nationwide could run into millions of euros.

The Paris prosecutor’s office told AFP that it had opened an investigation into what it described as a “large-scale cyber-attack affecting the refrigerators of several major food retail chains across France”.

European Commissioner for Agriculture and Food Christophe Hansen condemned the attack in a post on X, warning that food security required greater attention at all levels.

“Because the weaponisation of food has become a reality,” he added.

The full extent of the attack, including the total financial losses and the number of affected stores, remains unclear.